WASHINGTON -- A group of 40 US senators sent a letter to South Korean President Moon Jae-in and Japanese Prime Minister Shinzo Abe last week, underscoring the importance of trilateral cooperation in the face of rising challenges posed by North Korea and China.

The letter, dated Thursday, was sent before a military intelligence-sharing pact between Seoul and Japan was set to expire at midnight Friday.

South Korea later postponed the termination of the General Security of Military Information Agreement following Japan's willingness to hold working-level talks on the two countries' export control measures. The US has also called strongly for the two sides to salvage the deal.

The letter, signed by a bipartisan group led by Sens. Dan Sullivan and Chris Van Hollen, was written the same day the Senate unanimously passed a resolution reaffirming the importance of GSOMIA. Sullivan disclosed the letter's text on his website.

"While we recognize the complex history between your two great countries, we believe it is a critical time for Japan, the Republic of Korea and the United States to work together and deepen our economic, security and cultural relationships," the letter reads, without specifically mentioning GSOMIA.

"Disunity only provides the opportunity for countries, such as China and North Korea, to sow discord in our relationships in order to shift the balance of power in the Indo-Pacific away from freedom and toward authoritarianism," it continues.

The US alliances with South Korea and Japan are the "linchpin of security and prosperity in the Indo-Pacific region and help advance the cause of a more peaceful, prosperous and free world," the letter adds. (Yonhap)